Method of manufacturing a shell type transformer core for ballast structure



May 2. 1967 E. SCHWARZ ETAL 3,316,521

METHOD OF MANUFACTURING A SHELL TYPE TRANSFORMER CORE FOR BALLAST STRUCTURE Original Filed Aug. 8, 1961 5 Sheets-Sheet 1 2 20 22 P 3212 4'0 U I I p I I f I 42 I i H W f M W i; g FC+| F U! )H', i M .IJIW A472 v L \N: INVENTORS.

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METHOD OF MANUFACTURING A SHELL. TYPE TRANSFORMER CORE FOR BALLAST STRUCTURE Original Filed Aug. 8, 1961 3 Sheets-Sheet 2 5.20 l 2 [U W4 f l l' 1' Q4 1 1 m M, i 71) mi; N mm .m" LL 2 f w!" T I" {I W QTHIU; 15%;;

41W I! WV INVENTORS.

3 316 621 May 2, E. SC 7 METHOD OF MANUFACTURING A SHELL TYPE TRANSFORMER CORE FOR BALLAST STRUCTURE Original Filed Aug 8 1961 Z ETAL 3 Sheets-Sheet 5 INVENTORS. 566% dcwm a United States Patent tion of Illinois Original application Aug. 8, 1961, Ser. No. 130,170 pow Patent No. 3,177,455, dated Apr. 6, 1965. Divided and this application Sept. 18, 1964, Ser. No. 397,585 2 Claims. (Cl. 29155.61)

This invention relates generally to ballast structures and more particularly is concerned with the method of forming the core of a ballast intended primarily for ignition and operation of gaseous discharge lamps.

This application is a divisional application of Ser. No. 130,170 filed Aug. 8, 1961, now Patent No. 3,177,455, issued Apr. 6, 1965.

The construction of a ballast of the type described and claimed in US. Patent 2,558,293 requires an elongate electrical steel core normally made up of laminations of punched sheet steel stacked and assembled togethen The basic core is known as a shell type structure in which there is a central winding leg on which the coils or windin-gs are mounted side by side and there are two side legs spaced from the central winding leg and having yokes or bridging ends abutting the ends of the central winding leg and thereby providing a pair of parallel magnetic flux paths with the central winding leg providing the return common to both flux paths.

Generally the proportions of the core of these ballasts are such that the width of the central winding leg is approximately twice the width of either of the side legs since it will be carrying approximately twice the flux.

In the said Patent No. 2,558,293, the elongate iron core there shown was constructed of the so-called forced core variety in which the side legs and the end yokes are integral thereby providing a framing portion, and the central winding leg is forced into the center of the framing portion, thereby providing windows so that windings which are mounted on the central winding leg will fit between the wide legs and the central winding leg.

More recently, however, the cores have been manufactured from so-called scrapless laminations as taught, for example, in US. Patent 2,892,249 and others. Such cores are punched from strips of electrical steel with mating projections and then are rearranged in such a manner that the necessary end yokes, shunts and so forth are formed from the projections and notches thereby effecting great savings in material.

The primary object of the invention is to provide a novel method of forming a ballast construction of the character described in which the core is formed of scrapless laminations.

Other objects of the invention are to provide a novel method of forming a transformer core for a ballast structure of the character described in which the dies required for stamping the laminations are simple, the structure is economical, and the disadvantages normally attendant upon the manufacture of a transformer core are obviated.

Still a further object of the invention is to provide a structure in which the ends of the central winding leg are both of substantially the same width so as to enable more facile coil assembly.

Other objects will become apparent as a description of the method is provided and it will be seen that variations in the steps of the method can be made without departing from the spirit and the scope of the invention.

In the drawings:

FIG. 1 illustrates the layout of nested laminations along a strip of steel moving horizontally through the punch press in which dies such as progressive dies are used to punch out the laminations.

FIG. 2 is a semi-diagrammatic sectional view taken through a transformer core of the character concerned from the laminations stamped as shown in FIG. 1, with the laminations rearranged as will be described.

FIG. 3 is a circuit diagram of one form of ballasting circuit.

FIG. 4 is a similar circuit form of ballasting circuit.

FIGS. 5, 6, 7 and 8 are semi-diagrammatic views, each of which shows in its upper portion a fragmentary sectional view through a transformer using scrapless laminations and in its lower portion the arrangement of the laminations nested together in the manner that they are disposed at the time they are repetitively punched from a continuous strip of steel.

Generally, the invention herein is concerned with a method of manufacture of an iron core ballast in which the core is made up of laminations of the scrapless variety punched from a continuous strip of metal with the central winding leg and the outer or side legs nested during the punching process. The laminations are then stacked and rearranged in such a manner as to properly align the stacks to provide windows within which coils are disposed.

As mentioned previously, the primary characteristic of the structure described herein is that the ends of the central winding leg are the same width so that coils may readily be threaded upon the central winding leg from either end. In the case of previous structures, the central winding leg had a T-shaped configuration so that all of the coils or windings had to be threaded onto the central winding leg from one end.

In FIG. 1 there is illustrated a strip of electrical sheet steel in the process of passing through a punching machine, for example, and having the nested lamination parts punched therefrom. The strip of sheet steel is designated generally by the reference character 10, and it will be seen that a set of laminations comprising generally two outer or side legs 12 and a central winding leg 14 are punched in nested condition. This is a repetitious pattern along the length of the steel strip 10 so that the total scrap which results is very small. The scrap is marked S and is cross-hatched in order to enable the same clearly to be seen.

It should be noted at this point that laminations 12 and 14 are stamped with the grain of the sheet of steel. Therefore, the stampings could be made in either a horizontal or vertical progression as viewed in FIG. 1 depending upon the orientation of the grain. In actual production, however, the progression of stampings usually advances along the length of the strip of stock for this is the normal direction of the grain of the sheet of stock.

A set of laminations for a core are shown to comprise generally elongate E-shaped side legs 12 having lateral inward projections 16 and 18 at opposite ends thereof, with a third lateral projection 20 intermediate the ends thereof and a recess or notch 22 alongside the projection 20. The central winding leg 14 has a width A which is very close to two times the width B of the side legs in order to provide suitable flux carrying capacity. The projections 20, by virtue of the nesting of the lamination parts 12 and 14, will form cut'out notches 24 in the central winding leg, and the recess which is formed in the side leg between the end projection 16 and the intermediate projection 20 will comprise a seat or window 26 whose purpose is to accommodate one of the windings S of the ballast to be described.

The recess or notch 22 by virtue of its nesting arrangement with the central winding leg 14 will provide a pair diagram but showing a second of outward extensions 26 on opposite side edges of the central winding leg 14 adjacent the recesses 24. The length of the central winding leg 14 and the length of the side legs 12 are identical except that during the punching process, by virtue of the nesting arrangement, the central winding leg is offset from the other two extending to the right as viewed in FIG. 1 beyond the lateral projections or extensions 18. The lateral extensions 18, therefore, notch into the central winding leg 14 and produce the recesses or notches 28 on opposite side edges. The dimension of these notches 28 along the length of the central winding leg 14 which is identified as C ob- Viously will be identical to the dimension D of the lateral extensions 18. It is unnecessary that the dimension E of the end formation which will be designated 30 be the same as the dimension D and, as a matter of fact, in order to prevent the dimension C from being excessively large,

'it will be found that the dimension B is normally larger than the dimension D.

Between the extension 20 and the extension 18, the side members 12 will provide an elongate seat or notch designated 32 in which the windings P and S of the ballast to be described are adapted to be arranged.

In forming the core of the ballast, assuming that the lamination parts 12 and 14 have been arranged in stacks of desired thickness, the winding S is slipped over the left end and moved along the central winding leg until it abuts against the extension 26. The windings P and S in that order, are slipped over the right-hand end and moved along the central winding leg 14 until the winding P engages against the projections 26 and the winding S abuts against the winding P. The windings are chosen of a suitable number of turns and size wires so that they will be accommodated in the windows 27B and 32. The side legs, now stacked in lamination, are thereafter fitted upon the assembly comprising the central winding leg 14 and windings in the arrangement which is shown in FIG. 2 so that the inward extensions 20 are juxtaposed relative to the outward extensions 26, thereby forming a shunt designated 36 between the winding S and the winding P. Gap-s of suitable dimension are provided at 38. It will be obvious that the total dimension across the resulting core, which core is designated generally 40 in FIG. 2, is equal to A plus two F where F is the lateral dimension of the extensions 16 and 18. The clamping notches 42 which are formed in each corner of the core may be disregarded. If we assign the letter G to the dimension from end to end of the extensions 26 and the letter H to the width of the side legs 12 at the extension 24, it will be obvious that the limitations on the dimension of G and H are controlled by the total dimension A plus two F. G plus two H must equal A plus two F with slight modification to take care of the width of the gaps 38. The depth I of the notch 22 will equal one-half of G minus A. Likewise the depth K of the notch 24 is equal to H minus B.

Since the dimensions I and K are related, one can work out the necessary dimension F to accommodate a suitable width of winding which will give satisfactory dimensions I and K for a given structure.

With respect to the notch 28, it has been found that this is desirable since it appears beneath the winding which is intended to carry the leading current. Wave shape is thereby improved and saturation in the core is decreased.

Reference may be had to FIGS. 3 and 4 which illustrate the circuits in which the ballast of the type shown in FIG. 2 are intended to be used. These circuits are discussed in detail in said co-pcnding application so that such further details are herein incorporated by specific reference to said application.

The method of manufacture which has been described is advantageous in that the core is readily formed with a minimum of scrap and is easily assembled.

In the remaining figures of the drawings, composites are shown in order best to illustrate the manner in which the modified forms are punched as well as assembled. In each case, below the center line the core structure is shown in nested condition exactly as it would be punched from a moving strip of steel passing through a punch press. In the portions of the figures above the center line, the core structures are shown arranged at the time they are assembled in stack formation and provided with windings in order to provide the necessary ballast core structures for use with circuits of the type shown, for example, in FIGS. 3 and 4.

In FIG. 5, there is illustrated a ballast core 540 which is formed in a manner similar to that of FIG. 2. In this case, the central winding leg 514 also has its end dimensions, such as A, identical so that in assembling the ballast, the windings P and S may be readily assembled on the right-hand end by threading the same upon the central winding leg 514. Likewise the winding S is readily threaded over the left-hand end of the central winding leg 514 and moved to a position abutting extension 538 formed in the central winding leg 514. This structure differs from that of FIGS. 1 and 2 in the respect that it is desired that there be an additional small shunt 550 between the windings P and S and hence, the outer legs 512 are provided with inwardly extending extension 552 which because of nesting with the central winding leg 514 will give rise to the notches 554 that appear beneath the winding S This is advantageous in that the winding S is intended to carry a leading current and the presence of a reduced section will improve the wave shape. In the structure of FIG. 5, during the punching of the laminations, the central winding leg is nested to the left of the side portion 512 so that the lateral extensions 516 engage in the body of the central winding leg 514 and thus provide the formation 530 at the left-hand end substantially equivalent to the formation 30 of FIGS. 1 and 2 at the right-hand end. This means that there will be a much larger notch 528 beneath the winding S and because of the need for the shunt 536, cooperation between the extension 538 and the lateral extension 520 will produce an additional notch 522 in the side legs 512 outside of the winding S An additional notch 521 will be formed beneath the primary winding P which will not have any deleterious effect. Note that again the width of the lateral extension 516 as indicated at D is less than the width of the formation 530 as indicated at E.

FIG. 6 is a figure which is arranged similar to that of FIG. 5 illustrating a ballast core 640 formed in a manner not much different than the ballast 540. The only significant difference is that instead of a shunt 550, windings P and S are abutted, and in order to provide the necessary decrease in the amount of iron beneath the winding S in order to improve wave shape, a slot 654 is punched in the central winding leg 614. In all other respects, the similarity is obvious.

FIGS. 7 and 8 are arranged similar to FIGS. 5 and 6 except in each case the winding S is shown at the righthand end instead of the left. The cores 740 and 840 are substantially longer, and in each case there is a shunt 750 and 850 formed between the windings S and P in the same manner as in the case of the core 540 in FIG. 4. These two figures illustrate the manner in which dimensions may be varied and adjusted to meet certain requirements and conditions. Note, for example, that the right-hand end of the side legs 712 has the lateral extensions 718 much narrower than the opposite end lateral extensions 716. This gives rise to a notch 728 beneath the Winding S which is much smaller than the notch 528 of FIG. 5 and 828 of FIG. 8.

It is believed that no further explanation is necessary, and it is pointed out that the method of forming the magnetic core structure of the character described is simple and efficient.

What it is desired to secure by Letters Patent in the.

United States is.

1. A method of producing a shell type transformer re on-which magnetic flux coils are mounted which is comprised of individual laminations of electrical steel stacked and arranged together in a unitary core structure, and in which the individual laminations consist only of elongate central winding leg members and elongate side members, the side members having lateral projections perpendicular thereto of substantially the same width at opposite ends thereof, and having at least one central lateral projection on an inner edge thereof, said central winding leg having its end dimensions of the same width and provided with a lateral extension intermediate the ends thereof, and the central winding leg members are stacked and the side members also stacked and arranged with the central members to form the side parts of the core, the length of the side parts are equal and the extension on the central winding leg and those on the side legs being juxtaposed whereby to form at least one shunt on said core; said method comprising stamping said central and side laminations in a continuous process from a strip of electrical steel moving through a stamping machine in a pre-determined geometrical arrangement of said individual laminations along the direction of movement of the sheet which defines groups of said laminations, each group including one pair of side laminations and one of said central laminations, all nested together with the projections of the side members engaging in notches of the central member and vice versa, whereby such stamping results in a substantial reduction of waste, of forming the projections at the same time as stamping, of assembling the coils on the central winding leg by slipping one coil over an end of said winding leg and moving it along said leg until it abuts against said extension and slipping a second coil over the opposite end of said winding leg until it abuts against said extension, and thereafter stacking an assembly of laminations to form the core.

2. The method of claim 1 in which said strip of electrical steel is moved lengthwise through the stamping machine, with the stamping accomplished with the grain along the length of said strip during said lengthwise movement.

References Cited by the Examiner UNITED STATES PATENTS 3,010,185 11/1961 Hume 29-155.58 3,072,826 l/1963 Schwartz et a1. 336-165 XR 3,219,957 11/1965 Feinberg 336-165 JOHN F. CAMPBELL, Primary Examiner. R. W. CHURCH, JOHN CLINE, Assistant Examiners. 

1. A METHOD OF PRODUCING A SHELL TYPE TRANSFORMER CORE ON WHICH MAGNETIC FLUX COILS ARE MOUNTED WHICH IS COMPRISED OF INDIVIDUAL LAMINATIONS OF ELECTRICAL STEEL STACKED AND ARRANGED TOGETHER IN A UNITARY CORE STRUCTURE, AND IN WHICH THE INDIVIDUAL LAMINATIONS CONSIST ONLY OF ELONGATE CENTRAL WINDING LEG MEMBERS AND ELONGATE SIDE MEMBERS, THE SIDE MEMBERS HAVING LATERAL PROJECTIONS PERPENDICULAR THERETO OF SUBSTANTIALLY THE SAME WIDTH AT OPPOSITE ENDS THEREOF, AND HAVING AT LEAST ONE CENTRAL LATERAL PROJECTION ON AN INNER EDGE THEREOF, SAID CENTRAL WINDING LEG HAVING ITS END DIMENSIONS OF THE SAME WIDTH AND PROVIDED WITH A LATERAL EXTENSION INTERMEDIATE THE ENDS THEREOF, AND THE CENTRAL WINDING LEG MEMBERS ARE STACKED AND THE SIDE MEMBERS ALSO STACKED AND ARRANGED WITH THE CENTRAL MEMBERS TO FORM THE SIDE PARTS OF THE CORE, THE LENGTH OF THE SIDE PARTS ARE EQUAL AND THE EXTENSION ON THE CENTRAL WINDING LEG AND THOSE ON THE SIDE LEGS BEING JUXTAPOSED WHEREBY TO FORM AT LEAST ONE SHUNT ON SAID CORE; SAID METHOD COMPRISING STAMPING SAID CENTRAL AND SIDE LAMINATIONS IN A CONTINUOUS PROCESS FROM A STRIP OF ELECTRICAL STEEL MOVING THROUGH A STAMPING MACHINE IN A PRE-DETERMINED GEOMETRICAL ARRANGEMENT OF SAID INDIVIDUAL 